Cyclic carbonates are attractive and important compounds in a variety of fields. Their favorable characteristics include high solubility, high boiling and flash points, low odor levels and evaporation rates, low toxicities, and biodegradability. Cyclic carbonates are found useful as intermediates in organic synthesis, e.g. protection of 1,2- and 1,3-diols and the construction of structurally complex molecules. The alkylene carbonates produced react with aliphatic and aromatic amines, alcohols, thiols, and carboxylic acids. Under certain conditions, they can also undergo ring-opening polymerization.
A number of methods exist to synthesize alkylene carbonates. However, carbon dioxide insertion into the appropriate oxirane is the commercial method employed to synthesize the most common carbonate, [1,3]-dioxolane-2-one. This method includes reaction in the presence of various activating reagents such as alkylammonium halide catalyst (tetraethylammonium bromide) (U.S. Pat. Nos. 2,873,282 and 2,773,070).
It should be noted the synthetic procedures typically involve high pressure of CO2, high reaction temperature, and a stoichiometric amount of activating reagents. In recent years there has been much progress in the synthesis of cyclic carbonates by means of a CO2 fixation process. Acid base catalysts such as [ZnBr2(py)2], Mg—Al mixed oxides, and the Cr-salen/DMAP catalyst system, exhibit high activities in the promotion of the reaction of CO2 with epoxide in high efficiency. The palladium-catalyzed reaction of unsaturated alcohols and aryl halides with CO2 can also lead to a variety of cyclic carbonates by means of CO2-elimination/fixation process and shows a high degree of diastereoselectivity, enantioselectivity, and enantiospecificity. Allylic carbonates also transform to the cyclic carbonates in the presence of palladium catalyst by means of a CO2-recycling process (Yoshida M. et al, Chem. Eur. J. 10:2886-2893 (2004)).
It has also been shown that six- or poly membered alkylene carbonates can be synthesized by reacting five-membered carbonates with diols. In this regard, alkylene carbonates can be used in lieu of more traditional reactants such as dialkyl carbonates or phosgene. In such a process, the yield of alkylene carbonate produced is dependent on the boiling point difference between the reactant and byproduct diols (Clements J H. Ind. Eng. Chem. Res., 42:663-674 (2003)).
Finally, U.S. Pat. No. 6,838,530 describe the use of cyclic six-membered ring monomers for polymerization so as to form two or more different multifunctional acrylic materials.